This invention relates to a novel method for spot-knocking the electron-gun mount assembly of a CRT (cathode-ray tube).
In the maufacture of a CRT, it is the practice to electrically process the electron-gun mount assembly therein after the CRT has been completely assembled, exhausted of gases and sealed. One step in this electrical processing is spot-knocking, which involves induced arcing between adjacent electrodes, usually between the focus electrode and an electrode adjacent thereto. Arcing removes projections, burrs and/or particles which would later be sites for the field emission of electrons during the normal operation of the CRT.
In prior spot-knocking methods, the lower-voltage gun elements; that is, the heater, the cathode (K), the control electrode (G1), and the screen electrode (G2), are connected to the focus electrode (G3); and pulsed high voltages, of about twice the normal maximum operating voltage for the CRT, are applied between the anode and the interconnected gun elements.
In recent years, higher operating voltages are being used, with the result that higher spot-knocking voltages must be applied. These higher voltages produce arcs which can cause crazing of the glass neck of the CRT and can cause vaporized metal to deposit on the inside of the neck and on the insulator surfaces of the mount assembly. To reduce these adverse effects, processing times and voltages may be changed with consequent loss of processing capacity and/or increased cost of facilitation. In addition, separate G2-G3 and G3-anode spot-knocking procedures may be necessary.